The present invention relates generally to internal combustion engines and, more particularly, to an active electronic diagnostic system for automatically testing an engine exhaust system having a variable geometry turbocharger to detect and report exhaust system operation.
Turbochargers can be used to increase the efficiency of both Otto cycle and diesel engines by increasing the amount of oxygen available for combustion. Turbochargers generally consist of a turbine wheel mounted in the exhaust manifold and driven by the escaping exhaust gasses. The turbine wheel is coupled to a compressor, such that the turning turbine energizes the compressor to increase the pressure of the intake air supplied to the engine. The turbine recaptures energy from the expanding hot exhaust gasses to actuate the compressor. The compressor typically provides air to the engine""s intake manifold at pressures up to several times that of atmospheric. The pressurized air contains more oxygen per unit volume than unpressurized air, allowing for increased engine efficiency.
Variable geometry turbocharger systems (VGTs) have been developed to overcome a limitation of turbochargers having turbine inlet nozzles and compressor discharge nozzles of fixed shapes and dimensions. Such fixed geometry turbochargers contributed to increased engine efficiency at one point on the range of engine torque requirements, but not over the engine""s entire operating range. In other words, a fixed geometry turbocharger designed to optimize engine operation at high RPM and air volume flows will not perform as efficiently at low RPMs and volume flows, and vice-versa. In fact, operation of a fixed geometry turbocharger under conditions sufficiently far removed from its design point could actually decrease the efficiency of engine operation and contribute to engine damage. The usual solution, employing an intermediate range turbocharger, minimized the occasions when the turbocharger would perform inefficiently, but did not eliminate them. VGTs allow for variance in the geometry of the turbine inlet and compressor discharge nozzles to give the turbocharger an RPM/air volume flow range commensurate with the engine operating range, over which it increases/optimizes engine operating efficiency.
One advantage provided by a VGT is that the geometry of the turbine inlet nozzles and/or compressor discharge nozzles is varied by changing the cross-sectional flow area of the respective nozzle (i.e., by moving a portion of the nozzle housing) or by rotating the angle of the nozzle vanes (if the nozzle is of the vaned variety). One problem associated with VGTs is that they are prone to sticking. VGTs are, by their nature, positioned in a hostile environment of very hot gasses containing waste products of the combustion process. Build-up of partially burned hydrocarbons and particulate matter on the moving parts of the VGT system may cause them to stick. Also, stresses on the VGT parts arising from the extreme temperatures and temperature differentials experienced as hot exhaust gasses flow thereover may result in the moving parts jamming or sticking. Finally, the VGT is especially prone to wear damage as it consists of moving parts situated in a hostile environment.
If the VGT is sticking or jamming, the efficiency of the engine will be impaired. Improper exhaust back pressure will result in decreased fuel efficiency, and may further lead to the engine stalling and possibly even to engine damage.
There is therefore a need for a reliable system for detecting and diagnosing malfunctions in the VGT system. The present invention is directed towards meeting this need.
The present invention relates to an engine diagnostic system for detecting malfunctions in an engine system having a variable geometry turbine exhaust system. The engine diagnosis system includes a variable geometry turbine adapted to receive exhaust gasses exiting an engine, a variable geometry turbine position sensor operationally connected to the variable geometry turbine, a compressed air reserve, a pressure capsule pneumatically connected between the compressed air reserve and the variable geometry turbine, a pressure regulator pneumatically connected between the compressed air reserve and the capsule, a pressure sensor pneumatically connected between the pressure regulator and the capsule, and an electronic control module electrically connected to the variable geometry turbine position sensor, to the pressure regulator, and to the pressure sensor. The sensors may be integrally connected to the engine exhaust system, or may be part of a diagnostic station. The electronic control module is adapted to periodically initiate a preprogrammed variable geometry turbine diagnostic routine.
The diagnostic routine includes the operations of sending a sinusoidal control signal to the pressure regulator, determining the configuration of the variable geometry turbine, determining the pressure of the capsule, calculating the configuration of the variable geometry turbine as a function of the sinusoidal control signal, calculating the pressure of the capsule as a function of the sinusoidal control signal, determining if the pressure sensor is in calibration, determining if the pressure regulator is malfunctioning, determining if the variable geometry turbine position sensor is in calibration, determining if the variable geometry turbine is malfunctioning, and displaying the results of the test.
One object of the present invention is to provide an improved VGT system for maintaining the exhaust gas of an internal combustion engine system at an optimum pressure. Related objects and advantages of the present invention will be apparent from the following description.